What size sofa, rug and coffee table does your living room need?
Grab a tape measure; you only need two numbers. Measure the wall your sofa will sit against, then the distance from that wall to the one opposite, and you'll get sizes made for your room rather than for the showroom.
Sharing the room with a desk or a dining table?
Measure only the part of the room you're giving to the sofa and coffee table, and use those numbers above. Then leave about 60 to 90 cm between the back of the sofa and the desk or dining chairs, so the chairs can pull out and someone can still walk past without squeezing.
Your sizes
These are the proportions designers start from, not laws. If a radiator, a door or a window sits in an awkward spot, trust the room first.